Mysterious Subwoofer Thumping

My new Polk Audio sub woofer seems to have a life of its own. When everything is off (except the subwoofer), out of the blue, the unit begins to emit a series of thumping noises from the bottom, which resonate on the floor. Any ideas?

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I don't know which model sub, but it do know some subs have an "auto" setting to turn the amp on and off. It is often triggered by the audio input connection to the sub. You could have some noise in that line that occasionally triggers the amp to turn on and later turn off, or if there is a sensitivity setting for the audio signal it is set to low. A piece of equipment upstream of the sub could be producing a slight hum or have a ground loop, even when "off" / standby. Some equipment even when off or in standby mode will pass through a signal.

Without knowing more about your model sub and the rest of the system it is only guessing.

Do you carry a cellphone when you getsomewhere around it? I noticed whenever I carry my phone and get within 5-6 feet of my sub it thumps even with the rest of the equipment off. The sub is on standby at the time. Just saying!

Do you carry a cellphone when you getsomewhere around it? I noticed whenever I carry my phone and get within 5-6 feet of my sub it thumps even with the rest of the equipment off. The sub is on standby at the time. Just saying!

piquat: I have the PSW505 Sub-woofer. There is a single connection cable from the receiver to the subwoofer, as per manual instructions. The thumping comes on when everything is turned off (TV, DVD player, and Receiver.) Very strange and annoying. Thanks for your comment.

From your description I assume you connected similar to Figure 8 in the manual, either to the Line IN or LFE in with an RCA cable.

Does it happen every few minutes, or every 15 mins or more? I would first try switching the sub to "ON" vs auto, and see if it goes away. If it goes away, it is likely there is some noise in your connection to the sub that is tripping the auto on feature. The thump is the amp turning on and off. Make sure the line to the sub is away from any power cords or cable / Sat TV cables. These can transfer noise into the cable.

Even though everything is off, there can still be noise in the system or transferred into the cable. If you turn the the sub on with everything else off, see if you can hear a faint rumble or noise from the sub. You may have to get very close to it or put your ear up to it to hear it.

If you have another amplifier connected to a speaker, or even a boom box that has RCA input jack, I would try connecting the RCA cable going to the Sub to the other system instead. With everything else off, slowly turn the volume on the amp and speaker or boom box and see if you can hear any noise. If you hear noise, turn the volume down by about half, and try moving the RCA cable location and see if it gets louder or quieter. Move it away from any thing that is making it louder. If you don't hear any change, turn the volume up a little more a try again. This may be easier with two people.